The present invention relates to improvements in reclosable plastic bags, and more particularly to a bag wherein walls are formed of a first material and separate fastener strips of a different material are attached to the inner surfaces of the bag walls adjacent the top of the bag.
Plastic bags, pouches and containers of various types having interlocking pressure-sealable closures are well-known, commercially available items which are currently used for a variety of purposes. The demand for these bags is continuously growing as new uses for them are found, but also growing is the demand for a higher quality product that will reliably protect the contents of the package. Accordingly, great pressure has been placed on manufacturers of such bags to produce them in ever greater quantities while reducing the number of defects that occur in the manufacturing process, so that they are not only more reliable, but more economical to produce. Such containers may be formed in a variety of ways, with each method of forming having its advantages and disadvantages.
In one form of plastic bag, rather than having the fastener profiles integral with the material of the bag, the interlocking profiles are carried on fastener strips which are attached to the bag. This permits the use of a bag material of material characteristics for the bag and profiles of material optimum characteristics for the profiles, which may be quite different from that of the bag material. A problem arises in the manner of attachment of the profile strips to the inner surfaces of the bag wall, particularly when dissimilar materials are used and materials which are thermally incompatible in that the application of heat will not cause a bonding of the profile strip to the bag wall. This may occur when the bag material is multilayered and has a non-thermoplastic inner surface, such as a foil, is presented to the fastener strip. A problem also arises if the bag material has printing or other foreign elements on the inner surface which would interfere with the bonding. One manner of attaching profile strips to plastic is disclosed in U.S. Pat. No. 4,428,788, although the disclosure is limited to bonding by simultaneous coextrusion of the film and the closure device with an intermediate thermoplastic bonding layer. Another manner of attaching profiles to film is shown in U.S. Pat. No. 3,904,468 wherein a bonding with freshly extruded strips is shown and a still further method is illustrated in U.S. Pat. No. 4,341,575 wherein an adhesive is employed.
However, these arrangements have limitations requiring certain types of materials and certain conditions of formation. In the formation of reclosable bags, it has been found that two very important criteria must be met with one being the assurance that there will not be leakage past the fastener strips or profiles at their ends. Another important factor to be satisfied is that the reclosable fasteners be easy to reclose and this requires assurance that the profiles will remain in alignment at their ends so that they can be readily pressed together between the thumb and forefinger or by a slider if one is used.
It is accordingly an object of the present invention to provide a method and structure for a flexible plastic bag having reopenable profiles at the top wherein the fastener strips can be attached to the bag surface under a variety of conditions and the attachment structure be such that leakage at the ends of the profiles is prevented.
A still further object of the invention is to provide a reclosable bag structure utilizing interlocking profiles wherein the profiles are held in alignment at their ends and the structure holding them in alignment does not result in leakage past the fastener strips.